678 ADDITIONAL EXERCISES 



the seed from scab with slight expense and trouble. Add ^^'2 pound of formalin to 

 15 gallons of water and immerse the seed tubers for two hours. The seed tubers 

 are then spread in thin layers to dry promptly. After removing from the solu- 

 tion, cut and plant as usual-. 



Hot Water Method for Smuts (Jensen) (consult Freemen, E. M.: Minnesota 

 .Plant Diseases, p. 225). — Provide two large vessels, preferably holding at least 20 

 gallons. Two wash kettles, soap kettles, wash boilers, tubs or even barrels, will do. 

 One of the vessels should contain warm water, say at 110° to i2o°F. and the other 

 scalding water, at 132° to i33°F. The first is for the purpose of warming the seed 

 preparatory to dipping it into the second. Unless this precaution is taken, it will 

 be difficult to keep the water in the second vessel at the proper temperature. A 

 pail of cold water should be at hand, and it is also necessary to have a kettle filled 

 with boiling water from which to add from time to time to keep the temperature 

 right. Where kettles are used, a small fire should be kept under the kettle of scald- 

 ing water. The seed which is to be treated must be placed, half a bushel or more at 

 a time, in a closed vessel that will allow free entrance and exit of water on all sides. 

 Hence a gunny bag, or sac, can be used for this purpose. Now dip the basket, or 

 bag, of seeds into the water at 110° to i2o°F. and lifting it out plunge it into the 

 second vessel containing water at 132° to i33°F. After removing the grain from the 

 scalding water, spread it on a clean floor, or piece of canvas to dry. 



Corrosive Sublimate. 



Corrosive sublimate, 2 ounces. 

 Water, 15 gallons. 



Dissolve the corrosive sublimate in 2 gallons of hot water, then dilute to 15 

 gallons, allowing the same to stand five or six hours, during which time thoroughly 

 agitate the solution several times. Place the seed potatoes in a sack and immerse 

 in the solution for one and a half hours, and then spread to dry. 



Insecticides Used to Kill Insects 



Carbon Bisulpkid. — This inflammable and volatile liquid is used against grain 

 weevils and against the insects that are destructive to herbarium specimens. 



Crude Petroleum. — This is an oily inflammable liquid used against scale insects. 



Hellebore.- — This is a stomach or internal insecticide. It is not poisonous to man 

 as are the arsenical insecticides, and is used where there is danger of poison remain- 

 ing on parts to be eaten. It is often used on currants and gooseberries when the 

 berries are beginning to ripen. It is used in the dry form, and must be fresh 

 when used. 



Hydrocyanic Gas. — This gas is made by dropping potassium cyanide into sul- 

 phuric acid and water. The fumes are deadly to all kinds of animal life, and the gas 

 is used only in special cases. 



Kerosene. — This is an excellent contact insecticide. Pure kerosene, however, 

 will ordinarily burn the leaves of plants, consequently it is used in pure form when 

 trees are dormant, or against insects off' of plants as grasshoppers, household insects, 

 etc. 



Kerosene Emulsion. — This is probably the best form in which kerosene can be 

 used. A stock emulsion is made as follows: 



